Should You Use VARCHAR(255) for All Text Fields in MySQL?

mysql text field varchar long selection suggestion

In the database design, all text fields are often set to Varchar (255). However, there may be some shortcomings in this approach.

Although Varchar only stores the necessary characters, it is necessary to consider the processing method of the Varchar field. When the storage engine is transmitted to the SQL layer, the string is filled to the maximum length of the declaration.

This filling behavior can lead to a large amount of memory consumption, especially in temporary tables or when performing sorting or group operations. For example, under the UTF8 encoding, a short string of Varchar (255) occupies 11 bytes on the disk, but it takes up 765 bytes in memory.

In addition, field size does not directly affect the size or performance of the index. However, the string filled in memory affects the overall system performance due to increased memory occupation.

In order to reduce these challenges, it is recommended to adjust the size of Varchar according to actual data requirements. This can not only enforce application -related constraints, but also minimize memory overhead. Although the optimal varchar size of the postal address and other fields may be challenging, choosing a reasonable maximum length based on typical usage can bring significant benefits.

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